Automated industrial systems, e.g., autonomous robots, have been developed to be more self-sufficient since the emergence of the first manufactured robots over half a century ago. Unlike the earliest robots, contemporary devices require less human assistance; they are capable of independently functioning and completing tasks in various types of unstructured environments. However, bringing robots and humans into spatial proximity leads to the fundamental concern of how to ensure safety for the human. A heavy industrial robot with powerful actuators and unpredictably complex behavior can cause harm, for instance, by stepping on a human's foot or falling on him. Therefore, detecting the presence of moving objects in the vicinity of robots is crucial for ensuring the safety of people working near the robotic system.
One approach is to equip the robot with motion-detection capabilities. Various motion-detecting technologies exist, including passive infrared detectors (PIRs), Doppler microwave sensors, ultrasonic rangefinders, scanned laser rangefinders, vision-based systems, pressure-sensitive mats, and arrays of infrared emitter/detector pairs, which are known as “light curtains.” U.S. Ser. No. 13/243,253, entitled Ultrasonic Motion Detection and filed on Sep. 23, 2011 (the entire disclosure of which is incorporated herein by reference), describes systems and methods for adaptively detecting the real-time approximate range and bearing of moving objects utilizing ultrasound. In various embodiments, an ultrasound transducer comprises multiple ultrasound transducer elements. This arrangement permits detection with a full 360° field of view and is capable of detecting multiple moving objects at different distance ranges with different velocities in real time, while ignoring the presence of immobile objects as a static background. Systems in accordance with the '253 application can reliably detect the range and bearing of one or more moving objects, while ignoring stationary objects in the vicinity of, e.g., an autonomous robot, thereby protecting humans in the working environment.
Although a robot equipped with this type of presence-detection system can register the proximity of people and take appropriate safety measures, the people themselves do not know whether the robot is aware of them and will adapt its behavior accordingly. Individuals may be hesitant to approach the robot, which limits their ability to train the robot and participate in tasks that the robot carries out; this, in turn, limits robotic design, since robots must be configured to adapt and learn without the expectation of robust and routine interaction with humans.
Alerting individuals to a robot's awareness of their presence represents a challenging problem. Audible detection indicators are unsuitable for use in a noisy industrial environment, and cannot provide location-specific feedback to multiple persons, while a display screen visually indicating the objects detected by the robot cannot provide an immediate, unambiguous, location-specific indication of detection in a work environment that may extend 360° around the robot: display screens are difficult to read from a distance beyond the robot's action radius and have limited view angles. Screen displays are also costly both economically and in terms of computational overhead. Indeed, in an industrial environment filled with automated equipment having display screens, individuals passing by the robot may ignore the content of its display screen as irrelevant unless they intend to operate it.